1. Field of the Invention
The present invention relates to a seat which is rotatable about a vertical axis thereof.
2. Description of the Prior Art
One of conventional rotatable seats is disclosed in Japanese Utility Model First Provisional Publication No. 63-83058. The rotatable seat comprises a support unit for supporting thereon a seat proper. The support unit comprises a lower base member which is secured to a floor, an upper base member which is rotatable relative to the fixed lower base member, and an annular flat retaining member for retaining the upper base member on the lower base member. The upper base member is put on the lower base member having an annular flange portion thereof slidably received in an annular groove which is defined between the annular retaining member and the lower base member. However, the rotatable seat has the following drawbacks.
When the seat proper receives force to lay the same in a certain direction, a portion of the upper base member receives force to separate the upper base member from the lower base member in an upward direction and tends to be deformed. A reinforcing member can be attached to the upper base member for preventing the deformation. However, this makes the structure of the support unit complicated and increases the production cost.